Panels or sheets comprising oriented material chips, and especially panels made of oriented elongated wood strands, known as oriented strand board or oriented structural board (OSB) panels in the art, represent structural chip board panels having higher strength characteristics than chip board panels or sheets without purposely oriented chips. The chips or elongated strands that are used for forming such OSB sheets or panels in the ideal case have a length-to-width ratio or strand aspect ratio of about 10:1. Furthermore, such panels typically have a multi-layered construction.
Mechanical chip spreading machines are conventionally used for forming such multi-layered panels. The spreading machines furthermore include spreading heads that may include an apparatus for orienting the flat elongated wood strands, so as to deposit or spread the wood strands in a desired orientation for each respective layer forming the panel on a forming belt. This orienting of the strands is generally carried out by mechanically orienting the strands in one or more orienting chutes, shafts or passages, and then depositing the oriented strands onto the forming belt. In this context, improving the quality or precision of the orienting of the strands can achieve an increased bending strength of the resulting finished panel. Nonetheless, it has become more difficult to achieve a precise and uniform orienting of the strands, and especially the orienting of the strands in the longitudinal direction on the outer surface or cover layers of the panel. This is because the strand board production plants have been developed to ever greater production capacities, and because the typically utilized strands being produced are becoming longer, e.g. typically 100 to 150 mm long at the present time, and these strands exhibit greater variations or fluctuations in their strand width. These factors all make it more difficult to orient the strands uniformly, consistently, and accurately in the intended orientation.
The German Patent Laying-out Publication DE-AS 1,174,058 discloses a spreading head having disc rolls for orienting wood chips. Respective orienting passages or vertical shafts are formed respectively between adjacent discs. This is achieved in that the respective discs of the neighboring rotational shafts intermesh or engage centrally with each other while forming lateral through-flow interspaces or passages therebetween. In other words, the discs of one disc roll are located respectively in the centers of the axial spaces between the discs of the adjacent disc roll. According to the reference, the resulting through-flow interspaces or passages have a width that is slightly larger than the average length of the wood chips that are to be oriented and spread. As a result of the limited partial overlapping of the discs, large non-overlapping areas are formed between the discs of one disc roll shaft with through-flow spacings that are essentially twice as large as the average chip length, so that the chips are only inadequately oriented in these rather large areas.
Published European Patent Application EP 0,175,015 discloses a method and an apparatus for longitudinally orienting chips for the production of OSB panels. The apparatus includes a spreading head with disc rolls, whereby the discs of the adjacent disc rolls intermesh with each other in an overlapping manner, but only form through-flow spaces or passages on one side of a respective disc in a particular embodiment. Namely, the width of a respective through-flow passage is maximized to almost the spacing width between successive discs axially along a single disc roll by having the respective adjacent discs of adjacent disc rolls almost touching each other in the axial direction. That arrangement aims to achieve orienting or guide passages having the required confined orienting width over larger areas, i.e. with lengthened vertical guide surfaces. Thereby, the abovementioned non-overlapping double-width areas of the passages are avoided, and the desired orienting of the strands is ensured over a longer vertical distance or path.
However, with such an apparatus, a relatively accurate or exact longitudinal orienting of the strands is only achievable when operating with a particular determined through-flow or output quantity. Namely, the width and length of the respective orienting through-flow passages must be particularly adapted or designed for the through-flow rate or quantity that is to be processed by the apparatus. In the event varying or deviating through-flow rates arise in operation, the quality of the achieved longitudinal orientation will be impaired. Namely, with small through-flow rates, the proportion of smaller strands can fall at least partially un-oriented through the too-large through-flow passages. On the other hand, for large through-flow rates, an undesired separating effect of the different strand sizes can arise. Thus, it has been found that a uniform and consistent panel quality cannot be achieved when using such a conventional apparatus in connection with varying chip material through-flow rates.